1. Field of the Invention
The present invention generally relates to a method and a system for generating an image, in particular, to a method for composing a three dimensional (3D) image with a long focal length and a three dimensional imaging system.
2. Description of Related Art
A stereo camera consists of two lenses having the same specifications, and a distance between the two lenses is about 7.7 cm, thus simulating an actual distance between human eyes. Parameters of the two lenses, such as focal lengths, apertures, and shutters are controlled by a processor of the stereo camera. By triggering through a shutter release, images of the same area but of different perspectives are captured, and the images are for simulating a human left-eye image and a human right-eye image.
The left-eye image and the right-eye image captured by the stereo camera are displayed by a display device alternately at a frequency exceeding persistence of vision of the human eyes, and meanwhile with the switching of liquid crystal shutter glasses worn on the human head, a human being can view the corresponding left-eye image and the right-eye image with the left and right eyes. After being conducted to the cerebral cortex, the left-eye image and the right-eye image are fused into a single image by the cortical centre. Since the left-eye image and the right-eye image captured by the stereo camera may be slightly different in angles, a certain parallax exists between two object images formed on the retinas, and the object images of different perspectives in the two eyes can be fused by the cortical centre to make a human being have a three dimensional impression.
Currently, a simplified stereo camera is available on the market, in which a zoom lens is adopted as a main lens, and a wide angle fixed focal lens is adopted as the other lens to serve as a supplementary lens for the main lens. Such a stereo camera is capable of capturing a three dimensional image with a specific focal length, and can save the cost and simplify the structural design, thus achieving the purpose of being light, thin, short, and small.
However, since the stereo camera has to adopt a left lens and a right lens with the same focal length to capture images of the same scene simultaneously so as to make the captured images have a three dimensional effect, the simplified stereo camera only can capture a three dimensional image with a specific focal length. When a user stretches the zoom lens, only the main lens may capture a magnified image, and the supplementary lens will still capture a wide angle image, such that the two images captured by the stereo camera do not have the same content, and cannot be composed into a three dimensional image.